Silicone resin and photosensitive resin composition containing the same

ABSTRACT

This invention relates to photosensitive silicone resins and resin compositions containing the same. Silicone resins of this invention are characterized by that a triorganosilyl group represented by the following general formula (1)                    
     wherein R is a divalent organic group and R′ is a divalent group or a direct bond is linked to all or a part of the ends of the backbone of polyorganosilsesquioxanes. Photosensitive resin compositions of this invention are formulated from the aforementioned silicone resins and a photogenerator of acid. The aforementioned silicone resins and photosensitive resin compositions show excellent performance as resist materials for multi-level resist processes and for forming barriers of PDP and, on account of their excellent plasma resistance (resistance to O 2 -RIE), yield patterns of a high aspect ratio.

This application is the national phase under 35 U.S.C. § 371 of PCTInternational Application No. PCT/JP00/01955 which has an Internationalfiling date of Mar. 29, 2000, which designated the United States ofAmerica.

FIELD OF TECHNOLOGY

This invention relates to silicone resins and photosensitive resincompositions containing the same useful as resist materials.

BACKGROUND TECHNOLOGY

In the fields of a variety of electronic devices including semiconductordevices that require microfabrication, there is a rising demand forhigher density and higher degree of integration of devices and finerpatterning has become essential to meet this demand. Moreover, in plasmadisplay panels (PDP), barriers of a high aspect ratio, that is, a highratio of height to width, are in demand in order to have light of highluminance emitted by enlarging the electric discharge space for display.

A method for obtaining higher resolution in patterning is to use lightof shorter wavelength in patterning of photoresists. However, the use ofshorter wavelength poses a problem of the depth of focus (DOF) becomingreduced with a drop in sensitivity and aspect ratio. Multi-level resistprocesses have been proposed to solve this problem. According to aprocess of this kind, a material such as novolac and polyimide that canbe readily dry-etched by oxygen plasma is deposited by spin coating on asubstrate and planarized, a resist resistant to dry etching by oxygen isapplied to the surface of the planarized layer, a pattern is formed, andthen the pattern is transferred to the bottom layer by anisotropicetching by oxygen plasma. As this process yields patterns of a highaspect ratio, developmental works are being conducted extensively onresist materials resistant to oxygen plasma etching.

Resist materials utilizing silicone resins are known to be highlyresistant to oxygen plasma etching and, for example, compositionsconsisting of ladder type polysiloxane esters or polysiloxanessubstituted with epoxy-containing alkyl groups and a photosensitivecompound capable of generating acid upon exposure to light are proposedin JP 7-56354 (1995)A1 and JP 8-193167 (1996)A1. Moreover, resistcompositions containing photosensitive silicone resins that arepolysiloxanes to which a diazonaphthoquinonesulfonyloxy group and anazido group are linked are proposed in JP 6-27671 (1994)A1 and JP6-95385 (1994)A1.

As for the barrier (rib) of a plasma display panel (PDP), a process forconstructing a rib with the use of a paste formulated fromphotosensitive resins and inorganic powders to raise the aspect ratio isdescribed in JP 10-62981 (1998)A1. The photosensitive resins in questionare acrylic polymers and the like.

Polyorganosilsesquioxanes are occasionally abbreviated to polysiloxanesand they are known to occur in three types, that is, cage, ladder, andrandom. Their structures and methods of preparation are described indetail in the specifications of WO98/41566, JP 50-139900 (1975)A1, JP6-329687 (1994)A1, JP 6-248082 (1994)A1 and elsewhere. A method forintroducing functional groups to the ends of thesepolyorganosilsesquioxanes is also described in detail in theaforementioned WO98/41566.

An object of this invention is to provide photosensitive silicone resinswhich exhibit excellent performance as resist materials for multi-levelresist processes and for forming PDP barriers. Another object of thisinvention is to provide resist materials which exhibit excellent plasmaresistance (resistance to O₂-RIE) and form patterns of a high aspectratio.

DISCLOSURE OF THE INVENTION

This invention relates to silicone resins composed ofpolyorganosilsesquioxanes whose ends are partly or wholly linked to atriorganosilyl group represented by the following general formula (1)

(wherein R is a divalent organic group and R′ is a divalent group or adirect bond).

This invention also relates to the aforementioned silicone resinswherein the polyorganosilsesquioxanes have a repeating unit representedby the following general formula (2)

(wherein R₂ is an unsubstituted or substituted phenyl group) and theaverage number of repeating units is 2-5,000.

Furthermore, this invention relates to the aforementioned siliconeresins wherein the polyorganosilsesquioxanes consist of one type or amixture of two types or more selected from ladder type, cage type, andmixed cage-ladder type and the weight average molecular weight Mw is800-100,000 as determined by gel permeation chromatography (GPC) andcalibrated against polystyrene.

Still more, this invention relates to the aforementioned silicone resinswherein R is —R₁COOX₁— or —R₁COOX₁—Si(CH₃)₂—O— (wherein R₁ is thedivalent residue of a polycarboxylic acid or derivative thereof and X₁is a divalent group).

Still further, this invention relates to photosensitive resincompositions formulated from the aforementioned silicone resins and aphotogenerator of acid.

Finally, this invention relates to a process for preparing theaforementioned silicone resins which comprises treatingpolyorganosilsesquioxanes with X—Si(R₃)₂—Y or X—Si(R₃)₂OSi(R₃)₂—Y[wherein X and Y are groups capable of linking with carboxyl groups orfunctional groups capable of reacting with terminal OH groups orterminal OM groups is an alkali metal) of the backbone ofpolyorganosilsesquioxanes and R₃ is a monovalent organic group] to givemodified polyorganosilsesquioxanes containing X or Y at all or a part oftheir terminal positions, and treating the terminal groups witht—BuOOC—R₁—COOH (wherein t—Bu is t-butyl group and R₁ is the divalentresidue of a polycarboxylic acid or derivative thereof). The group R₃here is a monovalent organic group such as alkyl and aryl, preferablymethyl, and R₃ in a given molecule may be of the same kind or of two ormore kinds.

Photosensitive silicone resins of this invention are structurallypolyorganosilsesquioxanes to which a triorganosilyl group represented bythe aforementioned general formula (1) is linked to all or a part of theends of the backbone chain. The backbone chain may be represented by thegeneral formula (R₂Si₂O₃)_(n) and n designates the number of repetitionand is 2 or more. Preferable polyorganosilsesquioxanes have a repeatingunit represented by the aforementioned general formula (2) and theaverage number of repeating units is 2-5,000, more preferably 5-500. Thegroup R₂ is a monovalent organic group and may be a hydrocarbon groupsuch as aryl and alkyl and an alkoxy group, but R₂ is preferably analkyl group with 1-6 carbon atoms or an unsubstituted or substitutedphenyl group, more preferably a phenyl group.

In the triorganosilyl group represented by the general formula (1), R isa divalent organic group and, as indicated by the aforementioned generalformula (1), R may be said to contain the residue of a carboxylic acid.The group R′ designates a divalent group or a direct bond and, in thecase of a divalent group, it is linked on the other side to the terminalSi—O— group of polyorganosilsesquioxanes. The t-butyl group at the endof of the triorganosilyl group comes off to leave a free carboxyl groupbehind when it contacts the acid generated from a photogenerator of acidthereby enhancing the the alkali solubility of silicone resins and it isthis property that is utilized in patterning.

Carboxylic acids which give the divalent group R include monocarboxylicacids such as benzoic acid and acetic acid and polycarboxylic acids andthey are preferably polycarboxylic acids. Such polycarboxylic acidsinclude pyromellitic acid, trimellitic acid, phthalic acid,biphenyldicarboxylic acid, biphenyltetracarboxylic acid,biphenylhexacarboxylic acid, benzophenonedicarboxylic acid,benzophenonetetracarboxylic acid, diphenyl ether dicarboxylic acid,diphenyl ether tetracarboxylic acid, diphenyl sulfone dicarboxylic acid,diphenyl sulfone tetracarboxylic acid, diphenyl sulfide dicarboxylicacid, diphenyl sulfide tetracarboxylic acid, benzanilidedicarboxylicacid, benzanilidetricarboxylic acid, benzanilidetetracarboxylic acid,benzanilidepentacarboxylic acid, cyclohexanedicarboxylic acid,cyclohexenedicarboxylic acid, succinic acid, adipic acid, maleic acid,and fumaric acid.

In the case of polycarboxylic acids, the carboxyl group not linked tot-butyl group may be present as free carboxyl (—COOH) or in the form ofester or salt. In particular, it is preferable that one of the carboxylgroups forms an ester linkage with Si either directly or through adivalent group X as illustrated by t—Bu—OOC—R₁—COO—X—Si(Me)₂—. Here, thegroup R in the general formula (1) corresponds to R₁—COOX and X is adivalent group such as alkylene or arylene or a direct bond.

In case polycarboxylic acids is tricarboxylic or higher acids, at leastone of the carboxyl groups remains intact and it may remain so or it maybe converted to the neutral form such as ester and salt. Alkalisolubility becomes poorer if the carboxyl group in question exists inthe neutral form such as ester. The acid from a photogenerator of acidcontributes to enhance alkali solubility by dissociating the t-butylgroup and generating a carboxylic acid. In the cases in which patterningis effected by utilizing this phenomenon, there should desirably be alarge difference in alkali solubility between the exposed and unexposedregions and, for this reason, the free carboxyl groups are converted toesters, preferably to t-butyl esters by treating with t-butyl alcohol orderivative thereof.

The group R may contain not only the residue of a carboxylic acid butalso a part of the residue of a terminal modifier which modifies theends of polyorganosilsesquioxanes as described above. A suitableterminal modifier can be represented by X—Si(CH₃)₂—Y in which Y is afunctional group capable of linking to the backbonepolyorganosilsesquioxanes and X is a functional group capable of linkingto a group such as carboxyl. For example, a terminal modifierrepresented by X—Si(CH₃)₂—O—Si(CH₃)₂—Y [wherein Y is a functional groupsuch as epoxy capable of reacting with the terminal OH or OM group (M isan alkali metal)] reacts with polyorganosilsesquioxanes at one endthrough Y to give polyorganosilsesquioxanes containing X at the otherend. The X-terminated polyorganosilsesquioxanes then react with theaforementioned polycarboxylic acid or derivative thereof to give aproduct whose R contains —CH₂—CH(OH)— in case X is an epoxy group. Avariety of groups such as ester and amide can be formed by changing X.In the aforementioned terminal modifier, X and Y may naturally beidentical with or different from each other, but one of them needs to bereactive with the terminal group (or terminal group being generatedduring the reaction) of polyorganosilsesquioxanes and the other needs tobe reactive with a group such as carboxyl or derivative thereof. As isapparent from the above description, the backbonepolyorganosilsesquioxanes and the triorganosilyl group represented bythe general formula (1) are linked not necessarily through a siloxanelinkage but through an appropriate group.

Photosensitive silicone resins of this invention can be prepared byutilizing a known reaction. In the case of polyorganosilsesquioxanescontaining terminal silanol, for example, the terminal modification iseffected by treating the polymers with a monohalide such asX—Si(CH₃)₂—Cl. One of preferable procedures for terminal modification isto treat polyorganosilsesquioxanes such as silanol-free cage type and/orladder type octaphenylsesquioxane with a terminal modifier such as theaforementioned X—Si(R₃)₂—O—Si(R₃)₂—X in the presence of an alkali metalcatalyst to give X-terminated polyorganosilsesquioxanes.

A silicon atom in polyorganosilsesquioxanes and the silicon atom in aterminal modifier such as X—Si(CH₃)₂—Y tend to undergo exchange reactionand a procedure utilizing this property is also effective for terminalmodification. In this case, at least one of X and Y needs to be reactivewith a carboxyl group. Moreover, it is possible to effect theaforementioned reaction and the exchange reaction simultaneously byusing Y as a group capable of reacting with the end ofpolyorganosilsesquioxanes.

A preferable procedure for preparing silicone resins of this inventionfrom terminally modified polyorganosilsesquioxanes is, for example, totreat the terminally modified polyorganosilsesquioxanes with an acidicester prepared by the reaction of t-butyl alcohol with a polycarboxylicacid or derivative thereof such as acid anhydride in the presence of aquaternary ammonium salt as a catalyst.

Silicone resins of this invention have a weight average molecular weightof 800-100,000, preferably 5,000-50,000, as determined by GPC andcalibrated against polystyrene. The silicone resins in question aresolid at normal temperature and soluble in many organic solvents such asesters and ethers. Furthermore, silicone resins of this invention arepreferably polyorganosiloxanes represented by the general formula(C₆H₅S_(3/2))_(n) having a triorganosilyl group represented by thegeneral formula (1) at all or 10% or more of their replaceable ends, forexample, one triorganosilyl group for n=4-20, preferably one for n=2-8.

Silicone resins of this invention are best suited for use as positiveresist materials. In such end uses, it is possible to incorporategenerators of acid or a variety of additives in order to enhancesensitivity or improve heat or a plasma resistance.

Additives indispensable to photosensitive resin compositions of thisinvention are photogenerators of acid. Such photogenerators of acidinclude, but are not limited to, sulfonium salts such astriphenylsulfonium trifluorosulfonate, triphenylsulfoniumtrifluoromethaneantimonate, triphenylsulfonium benzenesulfonate, andcyclohexylmethyl(2-oxocyclohexyl)sulfonium trifluoromethanesulfonate,iodonium compounds such as diphenyliodonium trifluoromethanesulfonate,and N-hydroxysuccinimide trifluoromethanesulfonate. A detaileddescription of the chemical formulas and actions of thesephotogenerators of acid is found in the aforementioned JP 8-193167(1996)A1 and “New Development of Practical Polymer Resist Materials”, p.57 (in Japanese) published by CMC. A photogenerator of acid is normallyadded at a rate of 0.2-25% by weight of total solids.

An organic solvent is used to adjust the viscosity. Preferable solventsinclude, but are not limited to, Methyl Cellosolve acetate, propyleneglycol monoethyl ether acetate, methyl lactate, ethoxyethyl acetate,methyl pyruvate, methyl methoxypropionate, N-methylpyrrolidinone,cyclohexanone, methyl ethyl ketone, dioxane, ethylene glycol monomethylether acetate, and diethylene glycol monoethyl ether.

Photosensitive resin compositions of this invention contain theaforementioned photosensitive silicone resins and photogenerators ofacid as indispensable components and often contain solvents. Inaddition, it is permissible to incorporate surfactants, colorants,stabilizers, coating improvers, and inorganic powders as needed.

Photosensitive silicone resins of this invention and their compositionscan be used as resist materials and barrier materials of PDP. Althoughthere is no restriction on the mode of their use as resist material,they are best suited for multi-level resist processes.

According to a multi-level resist process, a material such as novolacwhich can be readily dry-etched by oxygen plasma is applied by spincoating to the surfaceof a substrate, a material of this invention isapplied thereto, the layers are exposed to a laser such as excimer togenerate acid from a photogenerator of acid and let the acid dissociatesilicone resins, patterning is effected by developing with an aqueousalkaline solution, and the bottom layer resist is etched by oxygenplasma to give a pattern of a high aspect ratio.

As for the preparation of barrier materials of PDP, methods such assandblasting, embedding, and photopaste are known. Since any of themethods uses photosensitive resist materials, materials of this inventincan be used as such. In particular, when applied to the photopastemethod or the like in which the resist remains unremoved, materials ofthis invention can fully produce the effect of excellent plasmaresistance.

PREFERRED EMBODIMENTS OF THE INVENTION Example 1

Phenylsilsesquioxane containg glycidyl group was synthesized withreference to Reference Example 1 and Example 3 described inPCT/JP98/01098 (WO98/41566) and JP 10-251407 (1998)A1.

Synthetic Example 1 Synthesis of Cage Type Octaphenylsilsesquioxane

In 500 cc of toluene was dissolved 105 g (0.5 mole) ofphenyltrichlorosilane and the mixture was shaken with water until thehydrolysis was completed. The hydrolysis product was washed with water,mixed with 16.6 cc (0.03 mole) of commercially available 30% methanolsolution of benzyltrimethylammonium hydroxide, and the mixture washeated at reflux temperature for 4 hr.

Thereafter, the whole mixture was cooled and left standing forapproximately 96 hr. After this time elapsed, the resulting slurry wasagain heated at reflux temperature for 24 hr, cooled, and filtered togive about 75 g of cage type octaphenylsilsesquioxane (C₆H₅SiO_(3/2))₈.In infrared spectrometry of the product, absorption bands assignable toSi—C₆H₅ were observed at 1595 cm⁻¹ and 1430 cm⁻¹ and an absorption bandassignable to the antisymmetric stretching vibration of Si—O—Si wasobserved at 1135 cm⁻¹ while an absorption band assignable to Si—OH wasnot observed at 3400 cm⁻¹. In ²⁹Si-MASNMR determination, only one sharpsignal of Si nucleus in the cage type octaphenylsilsesquioxane wasobserved at −77 ppm. The number average molecular weight Mn was 760 whendetermined by GPC with o-dichlorobenzene used as a flowing solvent andcalibrated against polystyrene.

Synthetic Example 2 Synthesis of Phenylsilsesquioxane OligomerContaining Glycidyl Group

To a reaction vessel were added 100 g of the cage typeoctaphenylsilsesquioxane, 70.3 g of1,3-bis(3-glycidoxypropyl)-1,1,3,3-tetramethyldisiloxane, 400 g oftoluene, and 4 g of tetramethylammonium hydroxide pentahydrate and themixture was heated at reflux temperature with vigorous stirring for 7hr. The reaction mixture was a white suspension at the start becausewhite powders of the the cage type octaphenylsilsesquioxane did notdissolve in toluene, but the powders gradually dissolved as the reactionprogressed and nearly all of them dissolved after 7 hr to give acolorless transparent solution. The solution was cooled to roomtemperature, a precipitate of the unreacted tetramethylammoniumhydroxide was removed by filtration, and the filtrate was poured into2,000 g of excess methanol to reprecipitate phenylsilsesquioxanecontaining a terminal glycidoxy group. The viscous precipitate waswashed with methanol and distilled to strip off the methanol and theresidual toluene to give 120 g of glycidyl-containingphenylsilsesquioxane oligomer as a pale yellow transparent viscousproduct. The epoxy equivalent as determined by the hydrochloricacid-pyridine method was 945 g/eq. The number average molecular weightMn determined by GPC and calibrated against polystyrene was 20,000.

Synthetic Example 3 Synthesis of Carboxylic Acid Containing t-ButylEster Group

To a 1-l three-necked flask were added 62 g of maleic anhydride, 74 g ofsodium t-butoxide, and 400 g of propylene glycol monomethyl etheracetate, 0.44 g of sodium methoxide was added as a catalyst, and themixture was heated under reflux at 150° C. for 2 hr. The mixture wasallowed to cool to room temperature and 0.85 g of concentratedhydrochloric acid was added. The resulting brown reaction mixture wasplaced in an eggplant-shaped flask and the solvent propylene glycolmonomethyl ether acetate was distilled off in an evaporator. Thereafter,the remainder was dissolved in 600 of dichloromethane andwashed with 500g of distilled water three times. The dichloromethane was evaporated offto give a carboxylic acid containing a t-butyl ester group as a brownviscous liquid in 90% yield.

Synthetic Example 4 Synthesis of Phenylsilsesquioxane Containing t-ButylEster Group

To a three-necked flask were added 100 g of the glycidyl-containingphenylsilsesquioxane oligomer prepared in Synthetic Example 2, 14 g ofthe carboxylic acid containing a t-butyl ester group prepared inSynthetic Example 3, 100 g of propylene glycol monomethyl ether acetateas a solvent, and 0.2 g of tetraethylammonium bromide as a catalyst andthe mixture was heated at 90° C. with stirring for 2 hr to givephenylsilsesquioxane containing a t-butyl ester group as a brown viscousliquid in 80% yield.

Example 2

(1) Experiments on Pattering Using Resins of this Invention

A photosensitive resin solution was prepared by dissolving 1 g oftriphenylsulfonium triflate (Ph₃S⁺OTf⁻) or a photogenerator of acid in100 g of a solution of the phenylsilsesquioxane containing t-butyl estergroup prepared in Example 1 in propylene glycol monomethyl ether acetateand the solution was applied by spin coating to a glass substrate anddried at 70° C. for 15 minutes to form a 0.3 μm-thick film. The film wasirradiated with UV (248 nm) through a mask and developed by a 3% aqueoussolution of tetramethylammonium hydroxide to give a clear pattern (lineand space 0.3 μm). It was confirmed that the resin exhibits a propertyof positive resist.

(2) Experiments on Two-level Resist Patterning Using Resins of thisInvention

A silicon wafer was spin-coated with a 1 a m-thick bottom resist layerof cresol novolac and a 0.1 μm-thick top positive resist layer of thephenylsilsesquioxane containing t-butyl ester group prepared in Example1, exposed to far UV (193 nm) excimer laser, and developed with a 2%aqueous solution of tetramethylammonium hydroxide to form a dear patternin the top layer (line and space 0.1 μm). Thereafter, the bottom resistwas etched by O₂—RIE and the top resist was removed by CF₄—RIE to formclearly patterned cresol novolac with a linewidth of 0.1 μm and anaspect ratio of 10.

Industrial Applicability

Silicone resins of this invention and their compositions give resists ofexcellent plasma resistance and make precision patterning of electronicdevices feasible. They are also well suited for barrier materials of PDPand, moreover, exhibit excellent performance as resist materials formulti-level resist processes and for forming barriers of PDP. Inaddition, they exhibit excellent plasma resistance (resistance toO₂-RIE) and, when used in patterning, give patterns of a high aspectratio.

What is claimed is:
 1. Silicone resins wherein a triorganosilyl grouprepresented by the following general formula (1)

wherein R is a divalent organic group and R′ is a divalent group or adirect bond is linked to all or a part of the ends of the backbone chainof polyorganosilsesquioxanes.
 2. Silicone resins as described in claim 1wherein the polyorganosilsesquioxanes contain a repeating unitrepresented by the following general formula (2)

wherein R₂ is an unsubstituted or subsituted phenyl group and theaverage number of repeating units is 2-5,000.
 3. Silicone resins asdescribed in claim 1 wherein the polyorganosilsesquioxanes consist ofone type or a mixture of two types or more seleted from ladder type,cage type, and mixed cage-ladder type and their weight average molecularweight Mw determined by gel permeation chromatography (GPC) andcalibrated against polystyrene is 800-100,000.